Biology Slide 1 of 24 End Show

advertisement
Biology
Slide
1 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
16-1 Genes and Variation
Slide
2 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
How Common Is Genetic Variation?
How Common Is Genetic Variation?
Many genes have at least two forms, or alleles.
All organisms have genetic variation that is
“invisible” because it involves small differences in
biochemical processes.
An individual organism is heterozygous for many
genes.
Slide
3 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Variation and Gene Pools
Variation and Gene Pools
A population is a group of individuals of the same
species that interbreed.
A gene pool consists of all genes, including all the
different alleles, that are present in a population.
Slide
4 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Variation and Gene Pools
The relative frequency of an allele is the number of
times the allele occurs in a gene pool, compared with
the number of times other alleles for the same gene
occur.
Relative frequency is often expressed as a
percentage, and it is not related to whether an allele
is dominant or recessive.
Slide
5 of 24
End Show
16-1 Genes and Variation
Variation and Gene Pools
Gene Pool for Fur Color in Mice
Sample Population
Frequency of Alleles
allele for
brown fur
allele for
black fur
Slide
6 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Variation and Gene Pools
In genetic terms, evolution is any
change in the relative frequency of
alleles in a population.
Slide
7 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Sources of Genetic Variation
Sources of Genetic Variation
The two main sources of genetic
variation are mutations and the genetic
shuffling that results from sexual
reproduction.
Slide
8 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Sources of Genetic Variation
Mutations
A mutation is any change in a sequence of DNA.
Mutations occur because of mistakes in DNA
replication or as a result of radiation or chemicals
in the environment.
Mutations do not always affect an organism’s
phenotype.
Slide
9 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Sources of Genetic Variation
Gene Shuffling
Most heritable differences are due to gene
shuffling.
Crossing-over increases the number of
genotypes that can appear in offspring.
Sexual reproduction produces different
phenotypes, but it does not change the relative
frequency of alleles in a population.
Slide
10 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Single-Gene and Polygenic Traits
Single-Gene and Polygenic Traits
The number of phenotypes produced for
a given trait depends on how many
genes control the trait.
Slide
11 of 24
End Show
16-1 Genes and Variation
Single-Gene and Polygenic Traits
A single-gene trait is controlled by one gene that
has two alleles. Variation in this gene leads to only
two possible phenotypes.
Slide
12 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Single-Gene and Polygenic Trait
Many traits are controlled by two or more genes and
are called polygenic traits.
One polygenic trait can have many possible
genotypes and phenotypes.
Height in humans is a polygenic trait.
Slide
13 of 24
Copyright Pearson Prentice Hall
End Show
16-1 Genes and Variation
Single-Gene and Polygenic Trait
• A bell-shaped curve is typical of polygenic traits.
• A bell-shaped curve is also called normal
distribution.
Slide
14 of 24
Copyright Pearson Prentice Hall
End Show
16-1
Click to Launch:
Continue to:
- or -
Slide
15 of 24
End Show
Copyright Pearson Prentice Hall
16-1
Which of the following statements is TRUE?
a. The relative frequency of an allele is not
related to whether the allele is dominant or
recessive.
b. Mutations always affect an organism's
phenotype.
c. Crossing over decreases the number of
different genotypes that appear in an
offspring.
d. Evolution does not affect the frequency of
genes in a gene pool.
Slide
16 of 24
End Show
Copyright Pearson Prentice Hall
16-1
Most inheritable differences are a result of
a. gene shuffling.
b. frequency of alleles.
c. mutations.
d. DNA replication.
Slide
17 of 24
End Show
Copyright Pearson Prentice Hall
16-1
The main sources of inherited variation are
a. gene shuffling and mutations.
b. gene pools and frequencies.
c. single-gene and polygenic traits.
d. genotypes and phenotypes.
Slide
18 of 24
End Show
Copyright Pearson Prentice Hall
16-1
A widow's peak in humans is an example of
a(an)
a. invariable trait.
b. single-gene trait.
c. polygenic trait.
d. mutation.
Slide
19 of 24
End Show
Copyright Pearson Prentice Hall
16-1
A graph of the length of the little finger on the left
hand versus the number of people having
fingers of a particular length is a bell-shaped
curve. This indicates that finger length is a
a. single-gene trait.
b. polygenic trait.
c. randomly inherited trait.
d. strongly selected trait.
Slide
20 of 24
End Show
Copyright Pearson Prentice Hall
END OF SECTION
Download